Taking for instance this handbook chapter:
I think that nowadays we can safely remove the language about APM as it is not used anymore.
Chapter 11.13.1 incorrectly states that acpi should not be compiled into the kernel while exactly the opposite is the case for the modern FreeBSD.
Same chapter advises to try to disable acpi as a debugging measure, but the most likely outcome of that is an unbootable system.
Generally, all the mentions of acpi.ko module should be changed to refer to the acpi kernel device. All advice on disabling acpi and apic should be removed.
We should change the language that describes ACPI as something new and buggy as nowadays ACPI is very well supported and tested.
Some of that medicine should also be applied to https://www.freebsd.org/cgi/man.cgi?acpi as well.